156 BULLETIK 82, UNITED STATES NATIONAL, MUSEUM. 



distal edges ; the last segment is short, without ambulacral structures, and is armed 

 dorsally with several recurved teeth, and the preceding one to three or more 

 segments may be more or less similar to it. 



Except for the first two the component segments may be sharply prismatic, as 

 in the Calometridse, Thalassometridaj, and Charitometridae, or they may bear 

 numerous long spines on their distal borders — a feature most conspicuous in Colo- 

 homefra, though more or less characteristic of all groups. Typically, however, they 

 are cylindrical, almost smooth, and very slender, with straight ventrolateral edges 

 and slightly everted distal ends, the eversion of the latter slowly increasing in 

 degree from the base to the tip. 



In some forms, as in certain species of Comissia, Coniatula, and Colobometra, 

 the ventral distal angles of the third and following segments may be produced into 

 a rounded flange-like process, or into a long spine. 



There is less variation in the first two segments than in those succeeding. They 

 may be somewhat elongated as in the Pentametrocrinida;, and they may appear to 

 be more or less enlarged in species in which the pinnules are exceedingly long and 

 slender, as in most of the Macrophreata. They never bear carinate processes, such 

 as are sometimes found, for example, in Comatella (fig. 1041, pi. 12), Gomatiila, and 

 Leptonemmter, and in the species of Calometridse (figs. 311, p. 223, and 314, 320, 

 p. 227), on the first two segments of the oral and lower genital pinnules. 



The distal pinnules in the multibrachiate comasterids are comparatively short, 

 never reaching the length of the oral pinnules, and are composed of short segments 

 which do not usually reach a length of more than twice the width, even distally. 

 The articulations are but little swollen, and the dorsal surface is more or less cov- 

 ered with fine spines, which become more prominent toward the distal border. The 

 recurved hooks on the terminal two to four outermost segments are strongly 

 developed. 



Wliile there is a very considerable average difference between the distal pin- 

 nules of the large multibrachiate species of Comasteridse and those of species of 

 other families — so much so that individual comasterid distal pinnules may at once 

 be identified as such — in the lO-armed young and in the 10-armed and smaller 

 species the difference becomes much less ; thus the distal pinnules of Leptonemaster 

 or of Comatilia have comparatively little that is distinctive about them. 



The distal pinnules of the species of Calometridse, Thalassometridse, and 

 Charitometridae are sharply triangular in cross section from the third segment out- 

 ward, and their component segments are relatively short as in most of the species 

 of Comasteridse. The pinnules as a whole are always relatively, and often abso- 

 lutely, short, as is well seen in the multibraciate genera, especially in the genus 

 Crinometra, so that they do not exceed the genital pinnules in length, and are con- 

 siderably less than the oral pinnules. In Parametra and in certain of the Charito- 

 metridae with very long arms the characteristic features of the distal pinnules may 

 become more or less obsolete at the arm tips, where the pinnules approach very 

 closely the usual slender elongate cylindrical type. 



There is very little difference in the distal pinnules of the remaining families, 

 and what difference there is is mostly correlative. For instance, if the arms are 



